NurbsPath and Beveling a BezierCircle
Checked out the file and was first rather surprised by how fast any slight movement of a point from the curves made a mess. Then if you think about it, small movements resulting in a very big mess very fast ... there is something wrong with the translation of action and reaction  .. yes the scale.

I checked and pretty much all curves even the circle (responsible for the size of the pipe diameter) had it's scale not applied. Or shall i rather say it was scaled in object mode, which is something pretty much everyone does and regrets later, more so when working with curves.

This:


Shows that the circle was scaled and the new scale was not applied, which for a straight path does not result in anything other then a thinner pipe.

Fixing this:


Press Ctrl+A -> "Scale"
Go in edit mode
Afterwards open the Sidebar with N and find the Transform panel, usually the top one.
Under Mean Radius it should be standing "1", but due to the previous steps it got changed to "4.123", set that back to "1" like so:

Circle profile fixed.


Now to the curves/paths.
There are a few things that need adjustments:


First it looks like this


The scale needs to be corrected, BUT here you need to be careful, as to not change the scale with the bevel object included!
Thus in the options, remove the Bevel Object resulting in this:

Now there are 2 things marked, rotation and scale. While we could just apply those, it would nip us in the butt afterwards, so believe me and do the following.
We have to leave the rotation alone! Applying it would mess with the sizes of the path internally.
And regarding the scale we have to do it manually.
Go in the Transform panel and change the value of the X-scale to 1. Just keep in mind it was 25.
After adjusting the scale the path will become very short 1/25th to be precise, so go in edit mode and press A selecting all elements, followed by S and then type in 25 followed by Enter. Resulting in the old length, without all the trouble.


Here is what would have happened if we had applied the scale or rotation or both, changing the path dimensions, thus causing more things to fix:

I know all can be fixed somehow, but let's fix to not have to fix the results, if you know what i mean ;)




Here how it does look now:


Now there are some settings you need to deactivate that only show their effect in edit mode, assuming that you want to have the pipe start and end with the path/curve and not generate a circle (endpoint connects to the startpoint, responsible for some of the weird shapes).


Deactivate the Cyclic U and Bezier U to get something like this:

As you can see the path is having it's normals along it's entire length, means with the Bezier circle applied as Bevel Object you now get something like this:



With this all done you can now move the points and get the expected results like shown here:



Ok long story short, scale is very important to pay attention to, if you want to adjust the sizes, it's recommended to do so in edit mode. Rotations i would also consider to adjust edit mode, as it can also cause issues, especially with the profile curve.

The other curves may have one or more of the same issues, but i believe if you followed the steps you should be able to handle those yourself now. Just beware, there you need to scale only in one direction.

When done, it should look like this:


All the steps you could have saved yourself by starting over with scale in mind, but since we are supposed to learn from mistakes, i believe it's good to know how to fix things and understand what caused the problem along the way.

Happy Blending.